As described by WO 2012/166413, a butterfly valve typically comprises a housing that has an inlet, an outlet and a flow path extending there through. A valve plate, located in the flow path, is typically configured to selectively allow and prevent fluid flow through the flow path. This is achieved by a shaft member being rotationally connected to the valve plate so as to enable the rotation of the valve plate perpendicular to the extension of the flow path.
Such butterfly valves are commonly used because they have the advantage of low cost, simple design, high stability and high efficiency. However, one problem faced by butterfly valves is that they require high opening and closing torques when the pressure drop across the valve is high. This typically limits the use of butterfly valves to services with a maximum pressure difference in the region of 30 bar.
To overcome this problem, various solutions have been developed including providing the valve with actuated opening plates. An example is provided in Canadian patent No. CA 2 058 427 C in which an actuated pivotal plate-like valve plate incorporated in the valve plate is discussed. WO 2012/166413 provides another such valve plate solution.
Each of these solutions adds significant complexity and therefore cost to the valve and therefore potentially lessens some of the potential advantages of a butterfly valve.
Another solution discussed in US patent application no. 2012/0256112 A1 involves providing a disk with a tilted disk that has a Z shaped disk vertical profile. In the open position such a valve has an increased profile that provides an increased resistance to flow.
None of these solutions provide complete solutions and so therefore there is a continued need to find alternatives that overcome the problem of high opening and closing torque requirements of a butterfly valve.